1. Field of the Invention
The invention relates to a method of selecting a generator matrix for encoding information words, comprising information symbols, into codewords of a code for providing an enhanced error correction capability if at least one information symbol is known a priori to a decoder decoding received, possibly mutilated, codewords. The invention relates further to a method of encoding information words into codewords, and to a method of decoding possibly mutilated codewords of a code into information words. Still further, the invention relates to a corresponding apparatus for encoding information words, to a corresponding apparatus for decoding possibly mutilated codewords, to a computer program implementing said methods, to a data carrier for recording user data and to a signal for transmitting user data.
2. Description of the Related Art
The concept of using a generator matrix for encoding information words into codewords is widely used and known, e.g., from Richard E. Blahut “Theory and Practice of Error-Control Codes”, Addison Wesley, May 1984, Sec. 3.2. Such a generator matrix is particularly used and described in standards, like the CD audio standard.
As a particular example for the use of a systematic algebraic code for the protection of information against errors, in the field of address retrieval on optical media, the sector address on optical media is part of a header which is protected by an error correcting code. Under many circumstances, e.g., if consecutive sectors are to be written or read, or in case of an enforced track jump to an approximately known disk area, much of the header information of the current sector can be inferred from the previously read sectors and the table of contents. However, for known codes, partial knowledge of information symbols hardly leads to an improved error correction capacity of the code.